Re: [PATCH] clocksource: sun4i: Clear interrupts after stopping timer in probe function

From: Chen-Yu Tsai
Date: Tue Jul 26 2016 - 02:42:30 EST

On Tue, Jul 26, 2016 at 1:49 PM, Maxime Ripard
<maxime.ripard@xxxxxxxxxxxxxxxxxx> wrote:
> On Tue, Jul 26, 2016 at 11:01:59AM +0800, Chen-Yu Tsai wrote:
>> The bootloader (U-boot) sometimes uses this timer for various delays.
>> It uses it as a ongoing counter, and does comparisons on the current
>> counter value. The timer counter is never stopped.
>> In some cases when the user interacts with the bootloader, or lets
>> it idle for some time before loading Linux, the timer may expire,
>> and an interrupt will be pending. This results in an unexpected
>> interrupt when the timer interrupt is enabled by the kernel, at
>> which point the event_handler isn't set yet. This results in a NULL
>> pointer dereference exception, panic, and no way to reboot.
>> Clear any pending interrupts after we stop the timer in the probe
>> function to avoid this.
>> Signed-off-by: Chen-Yu Tsai <wens@xxxxxxxx>
> Awesome, thanks!
> You should put stable in Cc though for this kind of patches.

AFAIK some maintainers prefer to add it themselves. Not sure about
clocksource so I left it out.